Why aren't you running the HDMI from the cable box to the Denon? Do you have photos of how you have things connected?
If that's the case you are only passing 2 channel to the external speakers. My suggestion is:... then out from there to out to my Denon AVR-5950H receiver. I then run the sound to my stereo speakers.
Your head is only spinning because you let yourself get caught up with bad information by both the people "helping" you on the phone, and the instruction book you found.Ok, my head is already spinning. Last evening I spent over two hours talking first with Denon (waste of time, as I learned at the end the guy was talking me through instructions he got from watching a YouTube video as we spoke. Sony walked me through a number of steps, none of which was helpful. Then the tv picture goes. I rebooted the cable box but it got stuck and never recovered. This morning I took it to Xfinity and got a replacement.
I set it up as follows, using HDMI cable: cable box>receiver>tv. I then called Sony again and we went through a couple of steps and got sound to come through the external speakers. But here's the rub: whether I got primary sound (such as dialogue) over background music and sound (secondary sound) differed from program to program. Even a show where there was primary sound, when a commercial went on the secondary sound predominated. The problem was the same on streaming services. On YouTube I got primary sound. On a DIsney+ show it was secondary sound.
I then found the instruction book online, which instructed me to plug the cable box into the tv, and then plug the tv into the receiver. This has allowed me to get primary sound, but only through the internal speakers. Nothing came out of the external speaker.
And g=gow do I determine if there is a center speaker and how do I get to it to turn it to off (assuming it is not already off).